A modulator of a conventional transmission apparatus is described below. FIG. 1 shows a modulator of a conventional transmission apparatus disclosed in FIG. 3 of Patent Literature 1.
An amplitude signal and a phase signal are input from input terminal 10-1 and input terminal 10-2, respectively. The amplitude signal is input to amplitude modulator 13 via variable delay section 11 that can change delay time. On the other hand, the phase signal, which is input to input terminal 10-2, is input to angle modulator 12, where the phase signal is angle modulated, and then, is input to the other input of amplitude modulator 13. Amplitude modulator 13 amplitude modulates the angle modulated signal output from angle modulator 12 with the amplitude signal output from variable delay section 11, and the output signal of amplitude modulator 13 is output from output terminal 17.
As described above, the configuration in which signal processing is performed separately on an amplitude signal and a phase signal, and these signals are amplitude modulated in a amplitude modulator is called “polar modulation.” In this kind of polar modulator, when there is a difference between the time in the path in which an amplitude signal passes and the time in the path in which a phase signal passes, a spectrum of the output signal deteriorates, so that it is necessary to accurately match these times each other.
In FIG. 1, control is performed using minimum amplitude detector 14, phase jump detector 15, delay control section 16, variable delay section 11, so that the delay time in each path matches each other.